Tuning indicator tube



@Cito 4, 1938. M NELSON 2,132,2I6

TUNING INDICATOR TUBE Filed July 51, 195e Patented Cet. 4, 1938 l UNITED STATES PATENT oF-EicE Application July 31, 1936, Serial No. 93,539

2 Claims.

My invention relates to 4electron discharge devices, more particularly to such devices useful as visual indicators of voltage and having an electrode which is rendered luminous, and has the appearance of afilament of light which may be of constant heightand varying intensity oi incandescence and'which changes in response to the change in the magnitude of the applied voltage, a device of this character being particularly useful as a tuning indicator in radio receiving sets.

It is an object of my invention to provide an electron discharge device of the kind described, which is particularly suitable for use as a visual tuning indicator in a radio receiving set Vand in which resonance is indicated by a brilliant lumi.- nous glow of an electrode.

VIn general my invention comprises an envelope having within it a straight lamentary anode and a pair of straight thermionic cathodes positioned on opposite sides of and parallel to said anode. Around each cathodeis mounted a straight tubular control electrodeparallel to the cathode and having a longitudinal slit opposite and parallel to the lamentary anode and through which electrons from the cathode are projected toward the anode to l'make it incandescent in response to electron bombardment. In operation the electrons owvfrom thev cathodes to the anode with suicient velocity to bombard the anode and render it incandescent. The control electrodes are so connected in a radio receiving circuit that when the circuit is tuned to resonance with an incoming signal the lamentary anode becomes incandescent while when the set is not tuned to resonance the anode is dark. The tube is sensitive to small changes in control voltage and in a properly designed circuit the anode can be changed from a dark color to bright incandescence with only a 2 volt change on the control electrodes.

'I'he novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims, but the invention itself will best be understood by reference to the following description taken in connection with the accompanying drawing in which Figure 1 is a perspective View of an electron discharge device embodying my invention with parts broken away to show details of construction; Figure 2 is an enlarged transverse section taken along line 2--2 of the tube shown in Figure 1; Figure 3 is a transverse section of a modification of Figurel 2; and Figure 4 shows a circuit arrangement us- (Cl. Z50-27.5)

ing a tube made in accordance with my invention.

The electron discharge device or tuning indicator tube shown in Figure 1 comprises van evacuated envelopel I provided with the usual v"5 stem and press II, and base I2.

`In accordance with my invention I mount vertically Within the` envelope a pair of parallel straight preferably oxide coated lamentary type thermionic cathodes I3 and support them at the i10 lower ends by means of lead and support wires I4 mounted in the press II, their upper ends by means of springs I5 electrically connected in series through the back support I6 mounted in the glass bead II, which is in turn supported by the back support I8 mounted on the press II. Positioned between these cathodes and coextensive with and parallel tov the cathodes is the filamentary type anode I9 which receives electrons from the cathodes I3 during operation of the tube. The filamentary anode preferably a une tungsten wire is supported at its lower end jfrom a lead-in and support wire and at its upper end by' a spring 2IA attached to the back support I8. Although I specifically show a la- 2 mentary type anode a strip of small mass could serve equally as well since it could be heated to incandescence by electron bombardment. To control the ilow of electrons from the lamentary l cathodes I3 to the anode. I9 I provide around each cathode a tubular control member 22 preferably of sheet metal provided with a slot or openings 23 parallel to and opposite the anode I9. The electrons from the cathodes I3 pass through the slots 23 to the anode I9. These control electrodes are supported at their lower end by means of a metal collar 24 supported in turn by the support rods 25 mounted in the press I I. While I show a pair of cathodes and control electrodes, a single cathode and control electrode can be used. The upper end of the electrode assembly may be properly spaced by means of the mica spacer 26.

In operation the voltage applied to the control electrodes 22, determines the intensity of incandescence of the anode I9. The less negative this control electrode 22 is biased with respect'to the cathodes I3, the brighter will be the incandescent portion of the anode I9, inasmuch as more electrons from the cathodes reach the anode than when the negative bias on the control electrode is large the electrons reaching the anode are fewer and the anode is dull red or dark. In this embodiment of my invention the incandescent porelectrons to get through the slots 23 to the anode I9. As the set is tuned to resonance the voltage difference between the cathodes and the electrodes becomes less, so that the control leffect ofl theY electrodes 22 on the electrons leaving the cathodes |3 is less, permitting more electrons from the cathodes I3 to reach the anode I9, so

that When the set is tuned to resonance the anode is incandescent and easily seen. Y

The application of an electron discharge de" Vice made in accordance with: my invention toa radio circuit is shown in Figure 4. Normally the cathodes I3, heated byrbattery 29, areelectrically connected through a biasing battery. 3D, to one side of a loadresistor 3|, the voltage across which is to be measured and which may for example be in the a.-V.-c. portion ofthe circuit.

The control electrodes 22 are connected tothe other side of the resistor 3 l; The anode voltage is supplied by battery 32. With no Voltage. onvthe controlelectrodes 22, veryA few electronsI and hence very little current flows through the tube between thev cathodes and anodes `due tothe biasing voltage on the control electrodes 22 and the anode is dark. Any-voltage dropacross resistor 3| is in, opposition to the biasing battery 3e. As the voltage drop across resistor 3| ncreases when the set is tuned to resonance `the effective biasing voltage on. the controlelecf trodes.22 decreases. Under these circumstances the control electrodes 22 become-less negative With respect to the cathodes I'3`,and more electrons go through the slots 23 to the anode. Thus Y the anode becomes incandescent as the negative bias on the control electrodes 22 decreases. characteristic of .the tuning indicator tube is made use of When'connected for example to a coni'fentional` automatic volume control circuit in which resistor 3| maybe placed.

In the modication shown in Figure 3 the'control electrode 2'I comprises two conductingkcyljo'pening in the side Wall through which the anode can be viewed.

While I have indicated the preferred embodiment of my invention of which I am now aware and have also indicated only one specific application for which my invention may be employed,

."itiwillbe apparent that my invention is by no meansv limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of my invention as set forth in the appended claims. i Y What I claim as new is: n Y

1. An electron discharge device having an envelope, a pair of straight parallel thermionic cathodes` within the envelope for emitting elec- Vtrons, a straight lamentary anode positioned between and parallel to said cathodes for receiving electrons from said cathodes, and a control electrode for each cathode vand comprising a tubular conductor partially surrounding .the

cathode and having parallel to the cathode and Opposite the anodean opening throughwhich electrons reach the anode.r Y

2.- An electron discharge device having an envelope, a pair. of rparallel straight thermionic f 

